Building a Yagi-Uda antenna

[Tommy Gober] built this Yagi-Uda antenna that has some handy design features. The boom is a piece of conduit with holes drilled in the appropriate places. The elements are aluminum arrow shafts; a good choice because they’re straight, relatively inexpensive, and they have #8-32 screw threads in one end. He used some threaded rod to connect both sides of the reflector and director elements. The driven elements are mounted offset so that a different machine screw for each can be connected to the appropriate conductor of the coaxial cable. The standing wave ratio comes in right where it should meaning he’ll have no trouble picking up those passing satellites as well as the International Space Station.

Pretty sure you’re out of line. Most antennas use the electro part of electromagnetic waves, so aluminum should be fine. Also, it’s not that aluminum is impermeable to magnetic fields, it’s that magnetic fields don’t interact with the metal much.
It’s an important distinction – if it was impermeable, you could use it to shield electronics from magnetic fields.

@washer
I think it’s a bit narrow to saw that this is “AARL stuff”. Most amateur operators I know today aren’t members, and have a bad taste regarding the AARL… Though I do agree, getting more people involved in amateur radio would be awesome.

That being said, the arrow shaft idea has been used for quite a while. In fact, Arrow Antennas (the guys I believe came up with the idea) sell many different versions of these for a very reasonable price. At first I was going to build one, but the parts cost almost as much as the antennas they sell, and their antennas are regarded as very good build quality.

“Wait… Aluminum is diamagnetic (pretty much impermeable to magnetic fields), right? Therefore the aluminum arrows would do absolutely nothing?

Or am I just on crack/way out of line?”

No, you’re just mixed up a little. Antennas do not need to be made of magnetic materials. All it takes to induce a voltage is for a conductor to be acted upon by a magnetic field. Think of it this way: Transformers are commonly wound with aluminum or copper, both non-magnetic materials. Both antennas and transformers are just devices designed to pick up induced voltage; a transformer is just MUCH more closely coupled. :)

Waffle you’re thinking correctly, it’s permeability (ability to form magnetic field in response to magnetic field). Aluminum is about the same as open air. But for a radio antenna this property doesn’t matter, conductivity is what you’re after. He needs to get some gold arrows!

The ARRL used to serve a very important role in the world of ham radio. But now, like many things from years past, it has been replaced by the internet.

Arrow Antennas have been around for ages, as someham mentioned. The dual band antennas are great because they make it easy to work dual band satellites, and a simple twist of the wrist corrects for (always changing for some sats) polarization.

This type of antenna is great for fox hunts, although some prefer a tape measure antenna (you don’t break it when you hit it on a tree or car door frame).

SWR is important, but it isn’t so much a measure of an antenna’s performance as it is it’s electrical match to the radio.

SWR basically measures the amount of power reflected back to the radio from the antenna due to an electrical mismatch. It depends, mostly, on the capacitance and resistance of the antenna (which is in turn based on the frequency of the signal).

Its black magic to me, but smith charts (wasn’t there a post about them awhile back?) can be used to describe the radiation pattern of a given antenna.

You can actually calculate the angle the RF leaves the antenna.

An example: a 2m J-Pole antenna can be tuned to the 70cm band (in other words it can have an SWR approaching 1:1), but the angle of attack (radiation pattern) of such an antenna is so bad that it makes the antenna almost useless at those frequencies.

Aluminum arrow shafts like this one and the ones from Arrow antenna are great. They are made from 7076 aluminum, which works a little like glass – you nick it with a file and snap it off. It is also stiff, as opposed to 6065 hobby tubing, which is just bends every which way.

Actually, you can use this for “digital signals”, which is actually analog radio waves modulated with digital bits of information.
People are using D-STAR into AO-27 to relay their “digital signals”. The ISS also serves as an APRS repeater which is a “digital signal”.

@norg
Last I checked, you can push digital signals wirelessly… including satellites as mentioned in the article. Besides, Yagis (coupled with very simple circuits) can be useful in locating RFI sources.

Bring more of ANY hack – the wider the focus, the better chances of learning more and mixing-and-matching dissimilar fields into something new.

@norg is probably a troll who thinks you need a ‘Digital T.V. Antenna’ to receive digital broadcast television channels. If you don’t like this kind of stuff don’t read it, maybe this site is more your speed http://www.hamsexy.com/ All harshness aside, I challenge you to study and pass your technician exam and get into amateur radio. Aside from communicating locally and around the world on lots of different bands (frequency ranges), in different modes, all on one radio (or more), there is much more than you could ever imagine to be learned in this hobby. BTW “cool wireless antennas” umm, all antennas either transmit or receive a wireless signal.

hook this up to your Wi-Fi data access point and give airplanes free Wi-Fi. from what i understand this type of antenna can double or triple the signal output… but im just pulling this out of thin air but it has some relevance think of your “CAN-tenna” there is math an equations im not built to remember or produce but it has something to do with dB/I and watts…

@norg
there is no such thing as digital signal, what you might call “digital” is analog signal modulated in specific way.
P.S. in times of disasters digital communication proof to be unreliable and it is analog one which save lives

@Daniel confuses a Smith Chart, which is a plot of impedance against frequency (from which you can derive VSWR), with a Polar Plot which shows the directivity of an antenna. Look similar, but very different.

Element conductivity is not nearly as important as the BALUN method used to transform the coax feed to/from the Driven Elements.

Yagi’s are great gain antennas for the home builder, I built a 2 meter, 5 element beam out of old TV antennas that I harvested for parts, and the SWR only goes from 1.2 to 1.4 across the band, not too shabby for free. I’m in a remote area, so now I’m gathering old TV antennas for the parts to build a 22 element 2 meter beam for our weekly simplex net (repeaters … who needs em).
73 –

Hi!need help in building a yagi uda Ant for a given assignment.
Complete noob at this!!!
Can someone guide here in building a 750Mhz operating Ant. with Beamwidth of around 90-120 degrees where elements are horizontally polarized.
Many thanks!